1. Field of the Invention
This invention relates to a power supply circuit and a display device provided with the power supply circuit.
2. Description of the Related Art
In an active matrix type liquid crystal display device that is manufactured by a low temperature polysilicon TFT (Thin Film Transistor) technology, a power supply circuit that generates an electric potential to control turning on/off of pixel TFTs has been formed on a glass substrate of a liquid crystal panel in order to reduce a cost of a driver IC (Integrated Circuit).
The power supply circuit includes a positive power supply generation circuit that doubles an inputted positive power supply electric potential VDD by a charge pump method to generate 2VDD and a negative power supply generation circuit that multiplies the positive power supply electric potential VDD by (−1) by the charge pump method to generate a negative power supply electric potential −VDD.
The positive power supply generation circuit and the negative power supply generation circuit are provided with a plurality of charge transfer transistors connected in series and a flying capacitor connected with a connecting node between the charge transfer transistors. Electric charges are transferred from an input side to an output side through the charge transfer devices by switching the charge transfer transistors in synchronization with a clock applied to the flying capacitor.
The active matrix type liquid crystal display device that incorporates the power supply circuit described above on the glass substrate is disclosed in Japanese Patent Application Publication No. 2004-146082.
With the power supply circuit described above, however, there is a case in which an unnecessary through current flows through the charge transfer transistor when the clock is inverted. When the unnecessary through current flows, an efficiency of the power supply circuit is reduced, resulting in insufficiency of output electric potential and increase in power consumption.